The invention concerns, in particular, the communication between two integrated circuits, e.g. via a USB connection. A USB buffer must in fact provide logic actions “1” and “0” at output, on a connection which can reach an output of 500 pF of capacitance, with a switching time of approximately 20 ns. The USB standard specifies that level “1” must have a voltage of 3V, whatever the mains voltage may be.
Normally, a USB buffer is just a power switch and is powered by a regulator delivering a constant 3V. This regulator must therefore have a very large output capacitor 15, in order to be able to support the peaks in current, in the region of 100 mA for 20 ns. In fact, it would not be able to react in 20 ns (as illustrated in FIG. 2) without this capacitor, and the voltage would then drop greatly without the latter.
FIG. 1 illustrates such a device. It therefore comprises a regulator 11, comprising an operational amplifier 111, which receives a Vbgap reference voltage on its positive terminal, for example, of 1.2 V. This operational amplifier 111 is connected to a transistor 112, this latter looping back to the negative input of the former, via a resistor 113. This regulator therefore delivers a DC voltage of 3 V to be regulated, with the aid of the external capacitor 14, which is directed in particular towards the buffer 12.
This buffer comprises two transistors 121 and 122, PMOS and NMOS respectively, which receive a command signal 123, and deliver on a resistor 124 the invention corresponding to the desired logic level.
As mentioned above, in order to obtain a response time below 20 ns, it is necessary to provide for an external capacitor 13, of a value of 500 pF for example. This necessitates providing for a specific output terminal on the integrated circuit, in order to connect this external capacitor 13.
Furthermore, such a capacitor increases the cost of the assembly, as well as the space required and the complexity of assembly.
Moreover, a regulator, assuming the presence of an operational amplifier, leads to a significant crowding of the surface of the integrated circuit.
The objective of the invention is in particular to reduce these various difficulties with the state of the art.
More specifically, one objective of the invention is to produce an integrated circuit capable of delivering a predetermined output voltage representative of a logic level, whatever the mains voltage, which does not require any external component, particularly a capacitor, to support peaks in current.
Another objective of the invention is to produce such an integrated circuit, which does not require the presence of a standard USB regulator, assuming the presence of an operational amplifier.
Another objective of the invention is to produce such an integrated circuit, which allows for simplifying the design, manufacture and assembly of the integrated circuit.
In other words, one objective of the invention is to provide a simple and efficient technique which uses little of the silicon surface, to produce such an integrated circuit.
The objective of the invention is also to produce such an integrated circuit, which offers a very short rise time up to the desired voltage, e.g. in the region of 20 ns.